Abstract
In the inductive power transfer (IPT) system, it is recommended to drive the resonant inverter in zero-voltage switching (ZVS) or zero-current switching (ZCS) operation to reduce switching losses, especially in dynamic applications with variable couplings. This paper proposes an improved autonomous current-fed push-pull parallel-resonant inverter, which not only realizes the ZVS operation by tracking the zero phase angle (ZPA) frequency, but also improves the output power and overall efficiency in a wide range by reducing gate losses and switching losses. The ZPA frequencies characteristic of the parallel-parallel resonant circuit in both bifurcation and bifurcation-free regions is derived and verified by theory and experiments, and the comparative experimental results demonstrate that the improved inverter can significantly increase the output power from 7.68 W to 8.74 W and has an overall efficiency ranging from 63.5% to 72.5% compared with the traditional inverter at a 2 cm coil distance. Furthermore, with a 2-fold input voltage (24 V), the improved inverter can achieve an approximate 4-fold output power of 38.9 W and overall efficiency of 83.6% at a 2 cm coil distance.
Highlights
Inductive power transfer (IPT) technology [1], characterized by convenience and safety, has many potential applications in portable devices [2], wireless sensor networks (WSNs) [3], implant medical devices (IMDs) [4,5,6,7], and electrical vehicles [8,9,10]
The slight difference between the measured and calculated results may be from the ignoring of the coils’ parasitic resistances and higher harmonics in the theoretical model. These results demonstrate that the improved inverter can track the zero phase angle (ZPA) frequency automatically, just as the traditional inverter does, which means the inverter can achieve zero-voltage switching (ZVS) operation as the coupling varies
This paper presents an improved autonomous current-fed push-pull parallel-resonant inverter in an IPT application
Summary
Inductive power transfer (IPT) technology [1], characterized by convenience and safety, has many potential applications in portable devices [2], wireless sensor networks (WSNs) [3], implant medical devices (IMDs) [4,5,6,7], and electrical vehicles [8,9,10]. It is often a great challenge to maintain ZVS or ZCS operation with variable couplings, caused by nonconstant coil distances, misalignment, shape deformation, or metal object proximity When it occurs to the frequency bifurcation region, the power transfer capability and efficiency can deteriorate rapidly at the original resonant frequency [2,13]. This method aims to keep the ZVS frequency fixed under coupling variation, it needs more switching devices, passive components, and even a complicated control unit. To achieve a cost-effective small-for-size IPT system, an autonomous current-fed push-pull inverter used in a parallel-resonant circuit structure was proposed in [20,21], and this system has the ability to naturally track the ZPA frequency of a parallel-parallel resonant network without any extra control or communication units. An improved inverter prototype is proposed, and the results are compared and analyzed with those of a traditional inverter
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